General IIR optical filter design for WDM applications using all-pass filters

A general design algorithm is presented for infinite impulse response (IIR) bandpass and arbitrary magnitude response filters that use optical all-pas s filters as building blocks. Examples are given for an IIR multichannel fr equency selector, an amplifier gain equalizer, a linear square-magnitude re sponse, and a multi-level response. Major advantages are the efficiency of the IIR filter compared to finite impulse response (FIR) filters, the simpl icity of the optical architecture, and its tolerance for loss. A reduced se t of unique operating states is discussed for implementing a reconfigurable multichannel selection filter.